The running properties of a tire, in particular of a pneumatic tire, are greatly dependent on the rubber composition of the tread, and particularly stringent requirements are therefore placed upon the composition of the tread mixture. A wide variety of attempts have therefore been made to improve the properties of the tire by varying the polymer components and the fillers in the tread mixture. A factor that has to be taken into account here is that an improvement in one of the properties of the tire often has the concomitant effect of impairing another property. Among the properties that are correlated, where improvement of one of the properties is usually attended by impairment of at least one other property, are the trio comprising abrasion, rolling resistance and wet grip.
The use of polybutadiene (BR) in rubber mixtures for tire treads can by way of example improve abrasion performance, but this is achieved by reducing wet grip. Another factor important for tires for commercial vehicles, however, is gasoline consumption, and the tires should therefore have minimized rolling resistance. Improvements achieved in the field of tires for commercial vehicles, for example, in terms of abrasion, should therefore as far as possible be achieved at the same level of rolling resistance.
U.S. Pat. No. 6,136,943 has already disclosed that abrasion performance and wet grip of a pneumatic tire can be improved by using, for the tread, a rubber mixture comprising from 50 to 90 phr of a rubber with a glass transition temperature Tg of from −110 to −80° C. for example, polybutadiene, from 10 to 50 phr of a rubber with a glass transition temperature Tg of from −7.9 to +20° C., for example, ESBR, and from 15 to 50 phr of a resin selected from the group consisting of hydrocarbon resins, phenol/acetylene resins, colophony-derived resins, and mixtures of these.
U.S. Pat. No. 7,084,228 B2 discloses, for improving the abrasion performance of pneumatic tires, the use of resins in the tread mixture in combination with from 40 to 100 phr of a diene elastomer with a glass transition temperature Tg of from −65 to −10° C., for example, SSBR, and from 0 to 60 phr of a diene elastomer with a glass transition temperature Tg of from −110 to −80° C., for example polybutadiene.
U.S. patent application publications 2004/0092644 and 2004/0122157 have already disclosed the combination of specific resins with rubbers with low glass transition temperatures Tg in tire tread mixtures for reducing abrasion in pneumatic tires.
The abovementioned specifications use polybutadiene as diene elastomer with a glass transition temperature Tg of from −110 to −80° C. The specifications do not explicitly disclose mixture constitutions that are usually used for treads of commercial vehicles.
EP 1 526 002 A1 discloses, for good ease of production, good durability, and good handling of pneumatic tires, a rubber mixture for the tread base which comprises at least one diene rubber, at least one filler, from 0.5 to 10 phr of at least one aromatic hydrocarbon resin, and from 1.5 to 10 phr of at least one fatty acid and/or metal salt of a fatty acid and/or fatty acid derivative. The examples reveal tread base mixtures with 70 phr of natural rubber, 30 phr of polybutadiene, and 2 phr of an aromatic hydrocarbon resin.